|Publication number||US7756416 B2|
|Application number||US 10/437,224|
|Publication date||Jul 13, 2010|
|Filing date||May 14, 2003|
|Priority date||May 30, 2002|
|Also published as||CN1283057C, CN1467945A, US20030223745|
|Publication number||10437224, 437224, US 7756416 B2, US 7756416B2, US-B2-7756416, US7756416 B2, US7756416B2|
|Inventors||Hiroaki Tomofuji, Takuji Maeda, Yuji Shimada|
|Original Assignee||Fujitsu Limited|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (17), Non-Patent Citations (2), Referenced by (4), Classifications (24), Legal Events (2)|
|External Links: USPTO, USPTO Assignment, Espacenet|
1. Field of the Invention
The present invention relates to an optical communication node and an optical network and, in particular, it relates to prevention of erroneous connection of optical communication nodes and optical networks having route switching functions in a wavelength division multiplex (WDM) network system.
2. Description of the Related Art
In recent years, as communication on the Internet, image transmission and the like becomes widespread, an WDM system that is suitable for large capacity and high speed data transmission using optical signals has been introduced. First, the WDM system has been introduced to long distance networks where the WDM system had much economic merit. At present, as its installation cost has been reduced due to the maturity of the technology, the WDM system is being introduced also in intracity core rings.
Conventionally, intra-company LANs between buildings and a metro-oriented system between suburb systems have been oriented to a ring network. As shown in
Today, WDM is applied also to the metro access network, wherein a passive OADM (optical add drop multiplexing) method is the mainstream method.
On the other hand, a signal that is input from the external network is converted into wavelength signals λ4-λ6 by the corresponding transponders 23-25, respectively. These are multiplexed into a signal of wavelengths λ4-λ6 by an multiplexer 22 and then added to the WDM signal of 32 wavelengths (λ1-λ32) transmitted on the fiber 10 via a fixed wave length filter 21.
As described above, according to the passive OADM method, any light signal of a particular wavelength or wavelength group can be readily added to or dropped from the WDM signal. However, since each node uses dedicated parts such as the fixed wavelength filters 11 and 21 that are adjusted for the corresponding devices, a signal path route (the wavelength or wavelength group to be used) assigned for each node is fixed.
As a result, in network design according to the passive OADM method, it is necessary to determine transmission routes and transmission capacity in advance and dispose filters for the determined conditions. Further, when the transmission routes or the transmission capacity are changed after the service is started, it is necessary to disconnect the network and terminate the service, and then add filters that correspond to new conditions.
In the future, it is expected that optical WDM ring networks will be introduced into the metro core network that is located between the access networks and the long distance networks. As shown in
In such a case, when data signals concentrated from the access networks are exchanged between the nodes, or line capacity is increased so as to connect to the long distance networks, for example, a technique for changing and switching line routes becomes important. It is expected that the paths (line routes) will be changed more frequently in the future and the switching will have to be performed automatically for the three reasons described below:
In consideration of the above facts, it is necessary to support features for flexibly accommodating disconnection of networks, suspension of service and the like due to the change of transmission routes or transmission capacity of the metro access networks and for performing switching of connection destinations remotely while preventing erroneous connection.
In normal communication, a transmitting end node A transmits a signal to a receiving end node D on a work path λx in the clockwise direction shown in a solid line in the figure by using the work signal. The receiving end node D receives the signal by selecting the work path. On the other hand, the corresponding protection path λx in the counterclockwise direction, that is shown as a dotted line in the figure, is idle.
Here, if any line failure, such as a break of the line, occurs in the work path, the transmitting end node A switches the path to the side of the protection path to continue transmission of the signal. After that, the receiving end node D also switches the path to the side of the protection path to continue reception of the signal. Here, it is to be noted that the signal interrupted by the line failure and the like must be recovered within 50-100 ms by the protection action.
In this connection, so as to improve operational efficiency of such configuration, path sharing is typically implemented by providing a signal PCA (protection channel access) path having a lower priority appropriately on the route for protection. In this case, when the failure occurs at the work side, the PCA signal is stopped at the protection side and a protection signal having a higher priority is inserted.
The line route switching occurs frequently and not only when the failure of the line route occurs but also when the line is operated normally due to the wavelength time-sharing service and the like.
In the switching of the line route setting described above, a network management system must manage the switching procedure and the switching timing and provide instructions appropriately but, conventionally, as shown below, there have been problems in that the erroneous connection of the paths might occur when the line route setting was switched, or operation of the instruction system for preventing such erroneous connection might be delayed.
In the case described above, relative switching timing of the line routes between the nodes A-D, or switching sequence of them will become a problem. When the switching is started from the receiving end node B, after the clockwise route is switched from the through mode to the drop mode at the node B and until the relay node A stops the transmission of the PCA signal and then is switched to the through mode, the PCA signal from the node A is erroneously connected to the receiving end node B and output to an external network.
On the contrary, when the switching is started from the transmitting end node D, the transmitting end node D first switches the line route to the clockwise direction. Then, after the relay node A stops the transmission of the PAC signal and then switches the route to the through mode and until the receiving end node B switches the route in the clockwise direction from the through mode to the drop mode, the signal from the transmitting end node D is erroneously connected to the node C that is the receiving end node of the PCA signal and output to the external network.
First, the node configuration in
The optical supervisory channel 33 converts the input signal into an electric signal to give it to a processing/controlling section 34 at the next stage. The processing/controlling section 34 checks communication conditions of the optical fiber 31 in the clockwise route relying on the input signal and the like, and if there is any failure, performs switch control inside the node and the like. Further, a pilot signal and others to be given to the node at the next stage are output via an optical supervisory channel 35 and an optical multiplexing section 36 at the output side.
Next, there will be given a description of the switching action in the node, wherein a work signal λ1 (w) in the clockwise direction that is demultiplexed by the optical branching filter 38 is input to a 2×2 switch 39. If the 2×2 optical switch 39 is set to an add/drop mode, it drops the input work signal λ1 (w) and outputs it to an external network 59 via an optical coupler 45 at the next stage and transponders 47 and 48 in a redundant configuration.
On the other hand, a signal from the external network 59 is input via either one of transponders 51 or 52, which are configured redundantly, and a 1×2 optical switch 50 to the 2×2 switch 39, which, in turn, adds the signal and outputs it as one wave in a WDM signal to the optical fiber 31 via an optical attenuator 40, an optical multiplexer 41, an optical postamplifier 42 and an optical multiplexer 36 at the next stage.
Alternatively, if the 2×2 optical switch 39 is set to a through mode, it passes the input work signal λ1 (w) and outputs it to the optical fiber 31 in the clockwise direction as one wave in the WDM signal via the optical attenuator 40, the optical multiplexer 41, the optical postamplifier 42 and the optical multiplexer 36 at the next stage. Its corresponding protection signal λ1 (p), that is input from an optical fiber 43 in a counterclockwise route, is handled similarly by a 2×2 optical switch 44.
Here, in the lower central part of the figure, it is to be noted that there is also shown an interface with the external network 59 of a direct connection type wherein the 2×2 optical switch is connected to the external network 59 directly, in place of the one of a transponder type wherein an optical signal is once converted into an electric signal and then converted into a predetermined optical signal. In this case, a WDM optical transmitter/receiver is incorporated into network devices out of the ring.
Next, based on the premise of the node configuration described above, the process of the erroneous connection shown in
On the other hand, if the transmitting end node D sets the 2×2 optical switch 44 to the add/drop mode and turns on the 1×2 optical switch 49 to start transmission in the clockwise line route, and then the relay node A switches the 2×2 optical switch 44 from the add/drop mode to the through mode, during the time when the receiving end node B switches the 2×2 optical switch 44 from the through mode to the add/drop mode, the signal from the node D is output to the external network 59 of the node C.
Further, if each node is instructed on switching procedures from the network management side in order to prevent the erroneous connection described above, there is a problem in that a load at the network management side may become excessively large and the time that is necessary for switching the line route in the entire node may be prolonged.
Therefore, in view of the above problem, it is an object of the present invention to provide a WDM ring network system that can prevent erroneous connection from a drop path of a node to an external network at the time of switching of a line route.
Further, it is another object of the present invention to provide a WDM ring network system that enables quick control and direction of network management in path switching and satisfies communication quality required for the ring network system that becomes increasingly large-scale.
In the large-scale WDM ring network system such as a metro core ring network, it enables support of prevention of the erroneous connection at the time of line route switching, and features for protection and for switching connection destinations remotely in connection with wavelength time sharing service that have been supported by a conventional SONET ring.
According to the present invention, there is provided an optical communication node that is connected to a specific optical path in an optical network, said optical communication node having: an external network that is placed thereunder; and an interruption means for interrupting connection between said optical network and said external network, wherein said interruption means interrupts the connection till a sequence of changing a route is completed when the route setting of said optical path is changed.
Said interruption means further interrupts the connection or releases the interruption in response to instructions from other optical communication nodes. Said optical communication node may further have an adding means for adding a receiving end node identifier to a transmitted signal, and a detecting means for detecting said receiving end node identifier included in a received signal, wherein said detecting means releases the interruption by said interruption means when said detecting means detects said receiving end node identifier of its own node.
Said optical communication node may further have a dummy signal means for generating and outputting a dummy signal, wherein said dummy signal means sends the dummy signal to said optical path and/or said external network to which signal transmission is stopped by said interruption means.
Still further, according to the present invention, there is provided an optical network system that interrupts at least one signal either from an external optical network to the input side of said optical network or from said optical network to the output side of the external optical network till a sequence of changing a route is completed when the route setting of an optical path is changed.
The present invention will be more clearly understood from the description as set forth below with reference to the accompanying drawings.
In step S101 of
Then, the line route is switched from the work side to the protection side to switch intra-device paths from a through mode to an add/drop mode. It prevents erroneous connection to the node C in subsequent processes. Then, a switching signal is transmitted to each upstream relay node residing on the line route at the protection side (the node A in this example), and an APS (auto protection switching) that is a switching control signal is transmitted to the transmitting end node D. Here, an optical supervisory channel (OSC) is used for transferring signals for path switching between the nodes.
In step S102, according to the switching signal received by each relay node, the intra-device paths are switched, if necessary. At this time, the node A interrupts connection with the external network 59 temporarily by means of the interruption means 62 so as to avoid signal leakage when the intra-device path is switched. In this example, the relay node A switches the clockwise route from the add/drop mode to the through mode. Further, it notifies the transmitting source node B of such switching.
In step S103, when the transmitting end node D receives the APS signal, the node D interrupts connection with the external network 59 temporarily by using the interruption means 63 so as to avoid leakage when the intra-device path is switched. Then, the signal transmission route is switched from the counterclockwise route at the work side to the clockwise route at the protection side. Then, the clockwise route is set to the add/drop mode.
In step S104, the transmitting end node D notifies the receiving end node B of completion of the path setting. In step S105, after the receiving end node B confirms receipt of a normal switching signal from each relay node (the relay node A in this example) and a path setting completion signal from the transmitting end node D, said interruption means 61 is released so as to permit the protection signal of a wavelength λ1 (p) to be output from the drop path to the external network 59. As described above, the interruption means 61 in the receiving end node B plays an important role in preventing the erroneous connection in this example.
Further, in each of transponders 47 and 48 at the drop side, an AIS generating section 72 and a switching section 73 that constitutes the interruption means of the present invention are newly provided. The AIS generating section 72 generates a dummy signal that consists of an alternating pattern of “1” and “0” values, and the switching section 73 selects a signal from either the conventional signal processing section or the AIS generating section 72 and outputs it to the external network 59. Here, when the switching section 73 selects the side of the AIS generating section 72, the connection to the external network 59 is interrupted.
With reference to the operation of the first embodiment, when a failure occurs in the counterclockwise line route, the signal processing section 34 detects the failure and the control section 71 controls the switching section 73 to select the side of the AIS generating section 72. Then, due to control by a 1×2 optical switch 53, a signal that is dropped from a 2×2 optical switch 44 at the work side is switched to a signal that is dropped from a 2×2 optical switch 39 at the protection side.
A 1×2 optical switch or an optical attenuator section 77 in the shutter card 74 interrupts a signal to the external network 59 in response to an instruction from the controlling section 71. Further, by connecting a transmitter for generating an AIS signal to one side of the 1×2 optical switch 77, a dummy signal may be output to the external network 59 at the time of interruption. The first embodiment operates similarly to the case shown in
In step S201 in
Here, it is to be noted that it is not absolutely necessary that the interruption means 61 interrupts the signal λ1 to the external network 59 in this example. Then, a request to stop transmission is sent to the transmitting end node of the signal to be dropped at the node B, and to the transmitting end node of the signal passing through the node B. In this example, the request to stop the transmission is sent to the transmitting end nodes D and A. An optical supervisory channel (OSC) is used for transferring control signals between the nodes.
In step S202, the transmitting end node D, and the relay node A that is disposed between the receiving end node B and the transmitting end node D and sends an PCA signal, receive said request to stop the transmission. The nodes D and A either interrupt the light transmitted from themselves by means of the respective interruption means 63 and 62, or transmit the dummy signal instead. Then, the nodes D and A notify the receiving end node B of completion of the process to stop the transmission.
Further, though not shown in
In step S203, the receiving end node B, which has received the notification of completion of the process to stop the transmission from the relay node A and the transmitting end node D, performs route switching in itself, and at the same time, instructs the nodes A and D to switch the route sequentially. In this example, as each of the nodes A, B and D performs route switching on the line route where there is no transmission signal or dummy signal, erroneous connection does not occur at the time of the route switching, as a matter of course.
In steps S204 and S205, the receiving end node B, which has received the notification of completion of the route switching from the relay node A and the transmitting end node D, releases the interruption means 61 in itself, and at the same time, notifies the nodes A and D of release of the request to stop the transmission. As a result, the interruption means 63 and 62 are released and the transmitting end node D starts signal transmission. As described above, the interruption means 63 and 62 in the transmitting end nodes D and A play an important role in preventing the erroneous connection in this example.
With reference to the operation of the second embodiment, when a failure occurs in the counterclockwise line route, the signal processing section 34 in the receiving end node B detects it and sends an APS signal to the transmitting end node D. The signal processing section 34 in the transmitting end node D, in turn, detects it and the control section 71 controls the switching section 73 to allow the AIS generating section 72 to output a dummy signal. Then, the 2×2 optical switch 39 at the protection side is switched to the add/drop mode and said dummy signal is input as an add signal.
Just as in the case of
In the first and second embodiments described above, the optical supervisory channel (OSC) is used for transferring signals for path switching, and each node transfers the control signals independently therebetween so as to control the interruption means 61-63 and path switches in each node. Therefore, though the problem of the erroneous connection is solved by the first and second embodiments, when the network scale becomes larger or paths across a plurality of ring networks are provided, the time for switching the line route is increased, which may result in degradation of communication quality.
In this embodiment, this problem is solved by configuring so that the control of interruption means 61-63 can be performed easily and quickly. For such purpose, an identifier is predetermined for each node and a transmitting end node transmits a signal with the identifier included in the transmitted signal. The receiving end node reads the identifier included in the received signal and, if the signal is destined for the receiving end node itself, the receiving end node releases the interruption means to connect the drop path to an external network 59. On the contrary, if the signal is not destined for the receiving end node itself, the receiving end node interrupts connection with the external network by means of the interruption means.
For example, when the transponders are used, the transponder at the transmitting side performs coding using the digital wrapper technology to set the identifier of the receiving end node in said header part. The transponder at the receiving side performs decoding accordingly and outputs the received signal if the signal is destined for the receiving end node itself. If the signal is destined for the other node, the receiving end node either interrupts the output or outputs a dummy signal to the external network.
Further, as an alternative method other than the digital wrapper, when the transponders are used in the transmitting end node and the receiving end node, a descrambling pattern that is provided for each receiving end node by the signal processing section may be assigned as a unique pattern and used as said receiving end node identifier. In this case, by associating the scrambling pattern that is provided by the signal processing section of the transmitting end node with the scrambling pattern of the receiving end node, a similar process can be performed in a way easier than said digital wrapper.
In this connection, when 2R transponders that do not perform retiming are used, or a WDM interface is provided at the side of network devices in the external network 59 to connect to the ring network directly without interposing the transponders (the direct connection configuration), the data signal itself cannot be manipulated such as by the digital wrapper technology described above and the like. In the present invention, in order to add receiving end identification information to the transmitted signal also in such case, a low speed pilot signal is superimposed on the main signal to be transmitted by amplitude modulation (AM), phase modulation (PSK) and the like.
According to this embodiment, in transponders 51 and 52 at the add side, a pilot signal transmitting section 85 is added to the conventional configuration. Instead of the digital wrapper signal shown in
With reference to the operation of the third embodiment, the transmitting end node D transmits a signal in which a pilot signal including identifier information of the receiving end node B is superimposed on a transmission signal from the external network 59. In this embodiment, said pilot signal is added to the 2×2 optical switch 39 via the 1×2 optical switch 49 and output to the clockwise line route.
Though an AIS generating section 72 and a switching section 73 that constitutes the interruption means of the present invention are provided in each of the transponders 47 and 48 at the drop side in this embodiment, a pilot signal receiving section 84 for controlling the switching section 73 is further provided in this example. The pilot signal receiving section 84 decodes the pilot signal (modulation signal) superimposed on the received signal and, if the information about the receiving end identifier specifies the receiving end node itself, controls the switching section 73 to select the side of the signal processing section. As a result, the interruption state is released. On the contrary, if the information specifies the node other than the receiving end node itself, the pilot signal receiving section 84 selects the side of the AIS generating section 72 to enter or maintain the interrupted state.
With reference to the operation of the third embodiment, the receiving end node B decodes the pilot signal included in the drop signal from the 2×2 optical switch 39 in the clockwise line route by the pilot signal receiving section 84 in the transponders. From the decoded result, the pilot signal receiving section 84 recognizes that the receiving end identifier information specifies its own node, and therefore controls the switching section 73 to select the side of the signal processing section. On the other hand, the relay node A recognizes that the signal is not destined for the relay node A itself from said decoded result, and therefore controls the switching section 73 to select the side of the AIS generating section 72.
When the first to third embodiments are applied to the connection between a plurality of ring networks, the path switching sequence according to each of the embodiments may be performed independently in each of the ring networks.
In the mesh network shown in
A switch 111 in the optical cross connect device 101 shown in
The interruption may be implemented by using the transponders 114 shown in
In the case of the third embodiment of the present invention, as described above, an identifier may be included in a signal, or alternatively, a pilot signal may be used. First, the case in which the identifier is included in the signal will be described. In this example, the identifier that corresponds to an intra-office interface of a specific port in the receiving end node C is inserted at the transmitting side of an intra-office interface of the transmitting end node D. When the receiving end node C detects the identifier of the own node at the receiving side of the intra-office interface, it outputs the signal to the external network. Further, information about the node through which the signal is to be passed may be included, and in this case, when the relay node detects its abnormality, the signal may be interrupted at the corresponding node.
On the other hand, when the pilot signal is used, the configuration shown in
As described above, according to the present invention, a WDM network that enables high-speed route switching without occurrence of erroneous connection is provided. As a result, prevention of the erroneous connection at the time of line route switching, a feature for switching destinations remotely in wavelength time sharing service and the like can be provided in a metro core ring network and the like.
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|U.S. Classification||398/2, 398/3|
|International Classification||H04B10/275, H04B10/291, H04L12/437, H04B10/07, H04B10/27, H04J14/00, H04J14/02, G02F1/00|
|Cooperative Classification||H04J14/0247, H04J14/0246, H04J14/025, H04J14/0252, H04J14/0283, H04J14/0284, H04J14/0295, H04J14/0226, H04J14/0297, H04J14/0227|
|European Classification||H04J14/02N4, H04J14/02M, H04J14/02P6S, H04J14/02P8|
|May 14, 2003||AS||Assignment|
Owner name: FUJITSU LIMITED, JAPAN
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:TOMOFUJI, HIROAKI;MAEDA, TAKUJI;SHIMADA, YUJI;REEL/FRAME:014073/0718
Effective date: 20030210
|Dec 18, 2013||FPAY||Fee payment|
Year of fee payment: 4